The
WHO Chinese National Influenza Center operated by the Chinese CDC in
Beijing released H1, N1, and MP sequences from 27 isolates from
Beijing, Shanghai and 11 provinces throughout eastern China. The
samples were collected between September 3 and December 4 from patients
who were almost exclusively under 65. Remarkably, 14 of the
sequences were from egg isolates and almost all had at least one of the
receptor binding domain changes that target human lung.

The high prevalence of
these receptor binding domain changes in the above egg isolates raises
concerns that the frequency of these changes is higher in 2013/2014
isolates than 2009, when pH1N1 emerged as a new pandemic. These
changes are also found at high frequency in egg isolates in the United
States, but the frequency of sequences from egg isolates is lower in
those released by CDC from US cases.

The criteria for the
pH1N1 isolate in eggs are unclear. If samples are placed on both
mammalian and egg cells, and sequences representing the H1N1 that grows
to highest titers, then the high frequency of egg isolates in China
would be cause for concern, because the vast majority of such isolates
have polymorphisms that clearly target human lung. It is likely
that the lower frequency of egg isolates in the US reflects collection
and isolation criteria, since high levels of severe and fatal cases in
the US have been widely reported.

Recent reports from California
and Texas
indicate the number of ICU and fatal cases in 2013/2014 will surpass
reported levels
in 2009, and these week 1 reports reflect H1N1 circulating after
the cases supplying samples for the released sequences from China and
the US.

More information on criteria for egg isolates in the US and China would
be useful.